1. Field of the Invention
The present invention relates to a conveyance apparatus for conveying a conveyance object with an endless conveyor belt.
2. Description of Related Art
Japanese Patent Unexamined Publication No. Hei 5-297737 discloses an inkjet printer including therein a conveyance apparatus having an endless conveyor belt being stretched between a drive roller and a slave roller. In the inkjet printer, an inkjet head ejects ink onto a paper being conveyed by the conveyance apparatus, to form a desired image on the paper. In this case, the resolution of the formed image in a conveyance direction of the paper depends on the conveyance accuracy of the conveyance apparatus. To form the image with a high degree of accuracy, therefore, it is necessary to accurately control the quantity of the conveyance of the paper. In the conveyance apparatus of the above publication, the conveyor belt is pinched by an encoder roller to which a rotary encoder is attached, and a pressing roller being biased toward the encoder roller. The drive of the conveyor belt is controlled on the basis of the rotational position of the encoder roller detected by the rotary encoder. In this manner, the rotary encoder can directly detect the quantity of the drive of the conveyor belt, and therefore, the conveyance quantity of the paper can be controlled on the basis of the drive quantity of the conveyor belt.
In the above-described conveyance apparatus, however, a deflection portion generated in the conveyor belt oscillates perpendicularly to the conveyance surface of the conveyor belt. The oscillation of the deflection portion may cause instantaneous displacement of the pressing roller. The instantaneous displacement of the pressing roller causes an instantaneous change in the pressing force of the pressing roller to the conveyor belt. The change in the pressing force of the pressing roller causes a sharp change in the contact pressure of the conveyor belt to the encoder roller. As a result, the encoder roller can not follows the movement of the conveyor belt, and the rotary encoder can not accurately read the conveyance quantity of the paper.